Digital electric power, or digital electricity, can be characterized as any power format in which electrical power is distributed in discrete, controllable units of energy. Packet energy transfer (PET) is a new type of digital electric power protocol disclosed in U.S. Pat. Nos. 8,068,937, 8,781,637 (Eaves 2012) and U.S. Pub. Pat. Application No. US 2017/0229886 A1.
The primary discerning factor in a digital power transmission system compared to traditional, analog power systems is that the electrical energy is separated into discrete units; and individual units of energy can be associated with analog and/or digital information that can be used for the purpose of optimizing safety, efficiency, resiliency, control or routing. Since the energy in a PET system is transferred as discrete quantities, or quanta, it can be referred to as “digital power” or “digital electricity”.
As described by Eaves 2012, a source controller and a load controller are connected by power transmission lines. The source controller of Eaves 2012 periodically isolates (disconnects) the power transmission lines from the power source and analyzes, at a minimum, the voltage characteristics present at the source controller terminals directly before and after the lines are isolated. The time period when the power lines are isolated was referred to by Eaves 2012 as the “sample period”, and the time period when the source is connected is referred to as the “transfer period”. The rate of rise and decay of the voltage on the lines before, during and after the sample period reveal if a fault condition is present on the power transmission lines. Measurable faults include, but are not limited to, a short circuit, high line resistance or the presence of an individual who has improperly come in contact with the lines.
Eaves 2012 also describes digital information that may be sent between the source and load controllers over the power transmission lines to further enhance safety or to provide general characteristics of the energy transfer, such as total energy or the voltage at the load controller terminals. One method for communications on the same digital power transmission lines as used for power was further described and refined in U.S. Pat. No. 9,184,795 (Eaves Communication Patent).
One application of a digital power distribution system is to safely distribute direct-current (DC) power in digital format and at elevated voltage from the source side of the system to the load side.
U.S. Pub. Pat Application No. 2016/0134331 A1 (Eaves Power Elements) describes the packaging of the source side components of Eaves 2012, in various configurations, into a device referred to as a digital power transmitter.
U.S. Pat. No. 9,419,436 (Eaves Receiver Patent) describes the packaging of various configurations of the load side components of Eaves 2012 into a device referred to as a digital power receiver.
In the receiver, the DC power is converted from digital format back to traditional analog DC format for use in commonly available power conditioning circuits. The Eaves Receiver Patent describes the employment of power conditioning circuits, widely known to the industry, to take an input voltage and produce a controlled alternating-current (AC) or DC output voltage. One example is a conditioner that takes a 380V DC input and creates a 12V DC output for use in a computer. A power conditioning circuit can also convert a DC input to an AC output, as is commonly found in uninterruptable power supplies or inverters. In its most basic form, a power conditioner is a simple switch that either allows or inhibits current flow. In another application, which is the subject of the present invention, digital power is converted in a receiver to be compatible with the voltage and current format necessary to charge a battery pack used for energy storage. More specifically, the battery pack may be incorporated into an electric vehicle, such as a warehouse lift truck or an electric automobile.
One aspect of the present invention is that the disclosed digital power charger system may manage the charging of multiple battery packs simultaneously. The concept of distributing power to various loads on a priority basis was introduced in U.S. Pub. Pat. Application No. 2015/0207318 A1, titled “Digital Power Network Method and Apparatus” (Lowe 2014). Lowe 2014 also introduced the concept of Power Control Elements (PCEs) to:                perform safe transfer of energy under digital power format;        convert from analog power to digital power under PET protocol, or vice versa;        convert and/or control voltage and/or current; and/or        switch power from one PET channel to another PET channel within the network.        
Lowe 2014 introduced the concept of power conditioning circuits within the PCE to convert and/or control voltage and/or current. The Eaves Power Elements invention further expanded on the definition of power conditioning circuits, including AC-to-DC and DC-to-DC conversion that is relevant to the charging system of the present invention.
Lowe 2014 is relevant to the present invention not only for establishing a framework for routing energy on a priority basis to multiple battery pack chargers, but also to introduce the concept of power control elements that are further incorporated into the digital power transmitter of the Eaves Power Elements invention. Thus, the system described herein is equipped with components to format the voltage and current to charge a battery pack, as well as to prioritize the allocation of charging energy to the individual battery packs. As described herein, a common bulk power supply in the transmitter supplies the minimum charge voltage needed for all of the battery packs attached to the system.
Advantageously, the system can utilize a centralized, high power, bulk converter that supplies the majority of the charging load for multiple battery packs. The bulk converter is supplemented by a lower-power, controllable, additive power converter assigned to each charge port. From an approximately 20%-90% charge state, many battery chemistries, such as lithium-ion, operate in a relatively narrow voltage range. The bulk converter provides the voltage necessary to support the lower limit of the charge state (e.g., 20%), which constitutes the majority of the power requirement. Heretofore, conventional charging systems provided dedicated power converters for each battery pack, leaving power conversion capability underutilized or “stranded” when the battery pack has completed charging. Moreover, during charging, the power drawn by the battery starts high initially and then continuously tapers down as the charging continues, again leaving power conversion capability stranded. By using a central bulk converter, the power capability of the converter can be redirected based on the demand of multiple battery packs, all of which may be at a different state of charge. Although a focus of this specifications is electric automobiles, the system can be utilized with any battery pack—such as would be used in warehouse lift trucks, aerial vehicles (drones), automatically guided vehicles or portable batteries for lanterns or battery powered tools.
Conventional charging systems for electric vehicles (EVs) are separated into “levels” according to their power capability, with a “level 1” charger being the least powerful and a “level 3” charger, also referred to as a DC fast charger, being the most powerful. EV owners often pay more for fast charging versus slower charging. Due to the cost and space required for a level 3 charger, it is often impractical for a customer that is not interested in paying for a fast charge to occupy a level 3 charger. This can result in restrictions to access to customers, or manual moving of vehicles between faster chargers and slower chargers, as when a vehicle has completed the fast portion of the charging profile. As discussed previously, the situation is exasperated when a new customer requires charging and another vehicle owner remains plugged in to a level 3 charger after the vehicle no longer is consuming energy at a high rate.
A previous multiport charging system disclosed in U.S. Pat. No. 8,810,198 (Nergaard) employs a centralized power unit that can switch in one or more internal power converter stages to an individual charging port. The connection of the power converter stages to a charging port is accomplished using electro-mechanical or semiconductor switches. If the demand from one charging port is higher than others in the system, Nergaard offers the advantage of being able to direct the combined power from multiple power converter stages to the high-demand battery pack. For example, if there are three charge ports available but only one battery pack being charged, then all three power stages can be dedicated to the single battery pack. However, only one battery pack can be connected to any power stage to prevent the undesirable condition of battery packs being electrically connected to one another. A disadvantage of the invention of Nergaard is that the power bus structure, the number of power stages and the number of power switches reach a high level of complexity and cost after only a few charge ports. In regard to power switches, if there are N power stages and M charge ports, there is a need for 2×N×M switches. In addition to the many switches, an internal power bus with attachments to each switch pole is needed for each charge port. Since only one power stage can be connected to a battery pack, then at least one full power stage must be allocated to each battery pack attached to the system, despite the fact that the battery pack may be demanding very little from the power stage.
The disadvantage of the many power switches and internal buses of Nergaard is somewhat overcome in U.S. Pat. No. 7,256,516 (Buchanan), where a single AC-DC power converter stage is combined with multiple DC-DC power converter stages, and where each DC-DC stage is assigned to one or more charge ports. However, in the invention of Buchanan, the summation of power ratings of the DC-DC power stages is greater than the rating of the AC-DC power converter stage, resulting in a relatively large and expensive charging system because, if only a small number of the available charge ports are occupied, then each DC-DC converter must be rated to utilize a substantial portion of the power made available by the AC-DC power converter in order to deliver satisfactory charging performance to each port.